The present invention was conceived to address problems affecting natural gas recovery from wells in the southern gas fields of Saskatchewan. The problems will be described in connection with those wells. However it will be appreciated that the invention may find application in other fields and wells.
The subterranean gas producing reservoir or formation involved is at shallow depth (about 340–695 feet). The wells are flowing wells. In a typical case, each well is cased with a string of 4″ tubular production casing to total depth and is perforated across a production interval of the formation. A string of ¾″ to 1-¼″ tubular continuous coil tubing extends down to the perforations. Some of the tubing strings are equipped with a packer. The packer seals against the casing to sub-divide the annulus between the two strings at a point above but close to the perforations.
In most wells, the producing formation produces salt water and particulate solids along with the natural gas.
The water is lifted by the gas up through the bore of the tubing string to ground surface in the form of alternating slugs of gas and water, under the impetus of formation pressure. However, slugs of water may settle in the tubing string and coalesce to form a column. This column may have a hydrostatic head that equals or exceeds the bottom hole pressure. In this event, the well will ‘die’. That is, additional fluid will be unable to enter the casing bore and fluid production from the well will cease.
The entry of particulate solids, such as sand, into the casing bore creates a different problem. The solids may settle in the annulus and build up at the base of the well until they cover the perforations, thereby interfering with incoming fluid flow from the formation.
It therefore is desirable to provide means for enhancing gas lift in the tubing string, with the aim of reducing settling and coalescence of the water slugs being produced.
It preferably also is desirable to enhance the turbulence of flow at the base of the casing bore, with the aim of reducing settling and build up of solids.